Window sashes are commonly mounted so they can be tilted inwardly to permit the outside glazing to be washed from inside the window frames. Wind force also urges the sashes inwardly. Accordingly, design objectives for tilting the sashes can be at odds with design objectives for wind resistance.
Double-hung window assemblies include upper and lower sashes that slide along sash runs between open and closed positions. The sash runs are often made from plastic jamb liners having front faces shaped for guiding the sashes, back faces resiliently supported from the window frames, and channels between the front and back faces providing clearance for sash counterbalance systems. The resilient supports, which include foam or spring backings, urge the front faces of the liners into contact with the sashes and provide a flexible seal between the sashes and the window frames.
Jamb liners for tiltable sashes include pairs of ridges for engaging plows formed in the sides of the sashes. Slots formed through the front faces of the liners separate outer and inner ridges of each pair for providing access to the counterbalance systems. Accordingly, each of the ridges is cantilevered from the front faces of the liners, and the liners are resiliently supported from the window frames. Although the ridges are sufficiently supported to guide the sashes under ordinary conditions, force can be used to tilt the sashes out of engagement with the ridges. The same direction of force can be applied by wind.
The wind force resistance problems of such tilt windows are difficult to solve because of the conflict between the need for easy tilting convenience and the need for strong wind resistance. The problem also becomes more severe as tilt windows are required to provide increasingly strong wind resistance so they can be certified to meet new standards.
Coassigned U.S. application Ser. No. 08/264,474, filed on Jun. 23, 1994, and which is hereby incorporated by reference, discloses use of braces for supporting outer ridges of the jamb liners adjacent to check rails of the lower sashes to improve wind resistance. The braces can be slid along the jamb liners away from the check rails so as to not interfere with sash tilting.
While suitable for many applications, care must be taken to return the braces to the check rail level to obtain the benefits of wind resistance. Also, the braces reinforce the jamb liners but do not limit compression of the jamb liners with respect to the window frames. Accordingly, improvements in wind resistance are limited.